1. Field of the Invention
This invention generally relates to fiber reinforced composites and particularly relates to preforms having woven strips of material used in reinforced composite materials, which can be woven flat and folded into their final shape.
2. Incorporation by Reference
All patents, patent applications, documents, references, manufacturer's instructions, descriptions, product specifications, and product sheets for any products mentioned herein are incorporated herein by reference, and may be employed in the practice of the invention.
3. Description of the Prior Art
The use of reinforced composite materials to produce structural components is now widespread, particularly in applications where their desirable characteristics are sought of being light in weight, strong, tough, thermally resistant, self-supporting and adaptable to being formed and shaped. Such components are used, for example, in aeronautical, aerospace, satellite, recreational (as in racing boats and automobiles), and other applications.
Typically such components consist of reinforcement materials embedded in matrix materials. The reinforcement component may be made from materials such as glass, carbon, ceramic, aramid, polyethylene, and/or other materials which exhibit desired physical, thermal, chemical and/or other properties, chief among which is great strength against stress failure. Through the use of such reinforcement materials, which ultimately become a constituent element of the completed component, the desired characteristics of the reinforcement materials, such as very high strength, are imparted to the completed composite component. The constituent reinforcement materials typically, may be woven, knitted or braided. Usually particular attention is paid to ensure the optimum utilization of the properties for which the constituent reinforcing materials have been selected. Usually such reinforcement preforms are combined with matrix material to form desired finished components or to produce working stock for the ultimate production of finished components.
After the desired reinforcement preform has been constructed, matrix material may be introduced to and into the preform, so that typically the reinforcement preform becomes encased in the matrix material and matrix material fills the interstitial areas between the constituent elements of the reinforcement preform. The matrix material may be any of a wide variety of materials, such as epoxy, polyester, vinyl-ester, ceramic, carbon and/or other materials, which also exhibit desired physical, thermal, chemical, and/or other properties. The materials chosen for use as the matrix may or may not be the same as that of the reinforcement preform and may or may not have comparable physical, chemical, thermal or other properties. Typically, however, they will not be of the same materials or have comparable physical, chemical, thermal or other properties, since a usual objective sought in using composites in the first place is to achieve a combination of characteristics in the finished product that is not attainable through the use of one constituent material alone. So combined, the reinforcement preform and the matrix material may then be cured and stabilized in the same operation by thermosetting or other known methods, and then subjected to other operations toward producing the desired component. It is significant to note at this point that after being so cured, the then solidified masses of the matrix material normally are very strongly adhered to the reinforcing material (e.g., the reinforcement preform). As a result, stress on the finished component, particularly via its matrix material acting as an adhesive between fibers, may be effectively transferred to and borne by the constituent material of the reinforcement preform.
Frequently, it is desired to produce components in configurations that are other than such simple geometric shapes as plates, sheets, rectangular or square solids, etc. A way to do this is to combine such basic geometric shapes into the desired more complex forms. In any such shapes, a related consideration is to make each juncture between the constituent components as strong as possible. Given the desired very high strength of the reinforcement preform constituents per se, weakness of the juncture becomes, effectively, a “weak link” in a structural “chain”.
While the prior art has sought to improve upon the structural integrity of the reinforced composite and has partly achieved success, there exists a desire to improve thereon or address the problem through an approach different from the use of adhesives or mechanical coupling. In this regard, one approach might be by creating a woven three dimensional (“3D”) structure by specialized machines. However, the expense involved is considerable and rarely is it desirable to have a weaving machine directed to creating a single structure. Another approach would be to weave a two dimensional (“2D”) structure and fold it into 3D shape so that the panel is integrally woven, i.e. yarns are continuously interwoven between the planar base or panel portion and other constituent portions.
The increased use of composite materials having such fiber preform reinforcements in aircrafts and jet engines has led to the need for composite conical shells. The traditional approach for forming a conical shell has been to generate a flat pattern 10 that is in the shape of a sector of an annulus, as shown in FIG. 1A. This shape is predisposed to take on the shape of a frustum of a cone 20 when it is folded so that the two straight edges 15 are aligned with one another, as shown in FIG. 1B. The flat pattern 10 can be cut from conventional 2D fabric, or can be woven directly into the annular shape using polar weaving equipment, for example.
Both methods, however, have certain limitations. Using 2D fabric results in a uniform thickness shell, with uniform distribution of fiber in two directions, but the fiber directions will not be aligned with the principle directions of the cone, i.e. the circumferential and axial directions. Polar weaving, on the other hand, will orient fiber in the principal directions, but the fiber distribution will vary in the axial direction. In either case, there will be a discontinuous seam where the two straight edges come together. Additionally, although the cone can have practically any dimensions, the maximum size that can be fabricated from a single flat pattern is limited by the size of the loom, and there can be substantial waste material if conventional 2D fabrics are used to produce the cone. Using a single piece of fabric is, however, desirable because it minimizes the number of seams and reduces the touch labor required to cut and position the fabric.